A cellular telecommunications system is based around cells or similar radio coverage areas. Examples of cellular telecommunications systems are well-known. In general, a cell coverage area or radio transceiver station coverage area of a telecommunications system can be defined as a certain geographically limited area covered by one or several base transceiver stations (BTS) serving mobile stations (MS) via an air or radio interface and usually connected to a base station subsystem (BSS). Each of the coverage areas of the system can be controlled by an appropriate controller apparatus. The controller is connected further to a gateway or linking apparatus, such as a gateway GPRS support node (GGSN) or gateway mobile switching center (GMSC), linking the cell to the other parts of the communication system. Several cells connected to each other cover a larger geographical area, and thus several cells form together the coverage area of a cellular telecommunications network.
Cellular telecommunications systems comprise a registration functionality in order to be able to control the movements and operation of the mobile stations subscribing to the cellular telecommunications network. Each station subscribing to a cellular telecommunications network is permanently registered in the network system which stores subscriber related data. This data may be the current location of the mobile station so that continuous track of the location can be kept for the purposes of call routing. In the GSM terminology, the permanent location registers are often referred to as home location registers (HLR). Each network may comprise one or several permanent or home location registers. The register can be a stand-alone network element or the register can be built into a network controller or into any other network element.
The permanent location register can also be implemented in a location server node. For instance, GSM based systems may include a gateway mobile location center (GMLC) which is used as both a permanent location register and a location service. This type of arrangement is particularly advantageous for subscribers who do not roam outside their home network, but may also be used for other types of subscribers.
In addition to the permanent registers, the cellular telecommunications networks comprise temporary or visitor location (VLR) registers. These temporary registers handle only temporary i.e. visiting subscribers, i.e. the mobile stations within the service area of the associated network controller at a given point of time. The temporary location register keeps track of the given service area within which the mobile station may be located and is constantly informed of whether the mobile station is ON or OFF. Each network controller may have its own visitor location register or the network controllers may share a stand-alone visitor location register or a visitor location register disposed within another network element.
The user equipment or mobile station communicates with an appropriate network controller and provides the controller with various kinds of information.
The use of cells or similar geographically restricted and known radio coverage areas and associated controllers facilitates the telecommunications system to produce at least a rough location estimate concerning the current location of an individual mobile station. More particularly, the telecommunications system is always aware (at least roughly) of the current location of such mobile stations which are communicating with at least one of the base stations of the system and are thus registered within at least one of the location registers of the system (i.e. are located within one limited radio coverage area of the system). This information is available even when the mobile station is located within a coverage area of a visited or “foreign” network, as the visited network is capable of transmitting the location of the mobile station back to the home location register, e.g. for the purposes of routing and charging. It is also possible to input location information provided by an external system for providing location information of a station into the telecommunications system, and to subsequently process and utilize this location information in the telecommunications system.
There have been proposed several techniques for providing the last known location of a mobile station, in particular with a time-stamp identifying when the location was calculated. This feature can be provided by a separate network element or server which receives the information from the various controllers of the system. More particularly, the determination of the location of the mobile user can be based on the location information received from databases of the visited controllers of the telecommunications system, e.g. from a visitor location register (VLR) in the GSM system. This type of arrangement would give the location to within of one base station or cell, i.e. it would indicate that the mobile station is (or at least was) within the coverage area of a certain base station or cell. The accuracy of the location determination can be improved by e.g. utilizing results of measurements which define the travel time (or travel time differences) of the radio signal sent by the mobile station to the base station.
A number of known techniques introduce disadvantages, particularly in increasing the signaling load in the communication system. In addition, regular and frequent updating of current location information requires additional memory resources in the communication system.
WO 01/28269 in particular discloses an improved technique providing location information of a user equipment. This technique applies a method wherein location information is not automatically provided to the location services.
Thus there is a compromise to be found between having the most up to date information for user equipment, with minimizing signaling and memory requirements in the system. As a result, location information for a particular user equipment may be out of date at a particular time it is requested.
A more particular problem arises when user equipment becomes disconnected from the network, for example because the user equipment has moved to a geographical are wherein there is no network coverage. In such a scenario, the last stored location information may be relatively old and unreliable.
It is an aim of the embodiments of the invention to address one or several of the above problems and also to provide a solution by means: of which the interaction of the location registers of a communication system may be made more efficient without causing excessive load to the system and/or by means of which a more efficient use of memory resources of the system can be achieved.